A method of controlling a fuel injection amount of an internal combustion engine includes a target injection amount calculation step, a component-by-component wear amount estimation step at which a component-by-component wear amount of an injector component is estimated, the injector component being a plurality of members or a part of the member constituting the injector and selected in advance as the injector component affects an accuracy of the fuel injection amount, a component-by-component correction amount calculation step, a total correction amount calculation step, and a total correction amount reflection step at which the injector injects a corrected target injection amount.